<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script src="jquery-3.5.1.min.js"></script>
    <input id="test-input" name="email" value="" placeholder="1">
    <select id="test-select" name="city">
        <option value="BJ" selected>Beijing</option>
        <option value="SH">Shanghai</option>
        <option value="SZ">Shenzhen</option>
    </select>
    <textarea id="test-textarea">Hello</textarea>

    <script>
        var
            input = $('#test-input'),
            select = $('#test-select'),
            textarea = $('#test-textarea');

        //input.val('abc@example.com'); // 'test'
        //input.val('abc@example.com'); // 文本框的内容已变为abc@example.com

        select.val(); // 'BJ'
        select.val('SH'); // 选择框已变为Shanghai

        textarea.val(); // 'Hello'
        textarea.val('Hi'); // 文本区域已更新为'Hi'

    </script>

</body>

</html>